[F-18]FDG PET/CT appearances of tumor thrombi in pediatric solid tumors

Objectives To elucidate the value of FDG PET/CT in detecting large tumor thrombi in the setting of pediatric solid tumors, and to describe the characteristic FDG PET/CT findings in tumor emboli/thrombi.

Methods Patients with clinical, or other radiographic evidence of tumor thrombus, who had undergone FDG PET/CT evaluation at our institution were selected and their medical records reviewed for demographic information, primary diagnosis, indication for FDG PET/CT, correlative imaging and clinical follow-up. In summary, after a minimum 4-hour fast, the patients received an IV injection of 0.15 mCi per kg body weight (min 2.0 mCi, max 12.0 mCi) FDG. Approximately one hour later, image acquisition began with a low dose CT for attenuation correction and lesion localization. The CT was followed by emission imaging using a GE Discovery LS PET/CT scanner in 2D mode at 5 minutes per bed position. Tumor thrombus SUVmax was measured and compared to primary tumor and blood pool SUVmax.

Results We identified 7 patients with a solid tumor and evidence of tumor emboli who had been evaluated by FDG PET/CT. Two patients had histological confirmation of tumor thrombus. Primary tumors were osteosarcoma (n=3), hepatoblastoma (n=2), high-grade sarcoma, and adrenocortical carcinoma (n=1 each). Tumor thrombi showed FDG avidity within the lumen of the right atrium, inferior vena cava, common iliac vein and pulmonary arteries (tumor thromboembolism). The SUVmax of tumor thrombus was < primary tumor, but > blood pool activity. Thrombi typically showed a linear pattern of intraluminal increased FDG uptake that could be heterogeneous in FDG avidity and configuration.

Conclusions In our series, FDG PET/CT could identify tumor thrombi and pulmonary thromboemboli developed in the context of various pediatric solid malignancies. A linear or focal pattern of increased intraluminal FDG uptake throughout the thrombus is characteristic of tumor thrombus